Cautious police chiefs are refusing to withdraw a legal challenge until the Government gives solid assurances over the future of Cleveland Police.

Cleveland Police Authority sought a "judicial review" to scupper the Home Office's plans to force through police mergers.

Last week, Home Secretary John Reid announced the planned enforced mergers would be scrapped.

But the authority is not withdrawing its judicial review bid until the Home Office gives assurances that controversial merger plans are scrapped.

Councillor Dave McLuckie, authority chairman, said he received a letter from the Home Office on Friday which confirmed police merger plans were binned.

But he added: "The Home Office letter is not enough," he said.

"All we want is for the Home Office to say in writing that forced mergers are being withdrawn, that they won't revisit mergers for at least 12 months and that they are prepared to look at alternative options for police forces."

A judicial review is the power of a court to review the official actions of other branches of government and has the authority to declare unconstitutional the actions of other branches.

A Home Office spokesman said: "As the Home Secretary made clear, enforced police mergers will not go ahead. All police authorities should have received written confirmation of that decision."

The police authority launched the legal challenge in February after former Home Secretary Charles Clarke warned police forces they would have to volunteer to merge or have mergers forced upon them.

The authority had fought against the merger plan which would have created a regional force of Cleveland, Durham and Northumbria. The Home Office refused to consider the alternative of a Tees Valley Police force.